Sweat sensing technologies have enormous potential for applications ranging from athletics, to neonatology, to pharmacological monitoring, to personal digital health, to name a few applications. This is because sweat contains many of the same biomarkers, chemicals, or solutes that are carried in blood, which can provide significant information enabling the diagnosis of ailments, health status, toxins, performance, and other physiological attributes even in advance of any physical sign. Furthermore, sweat itself, and the action of sweating, or other parameters, attributes, solutes, or features on or near skin or beneath the skin, can be measured to further reveal physiological information.
In particular, sweat sensing devices hold tremendous promise for use in workplace safety, athletic, military, and clinical diagnostic settings. A primary goal of the disclosed invention is to provide decision support to a sweat sensor system user that is informative at the level of the individual patient. A sweat sensing device worn on the skin and connected to a computer network via a reader device, such as a smart phone or other portable or stationary computing device, could aid in recognition of the physiological state of an individual, and relay crucial data about physiological states. In certain settings, sweat sensing devices may continuously monitor certain aspects of an individual's physiological state and communicate relevant information to a reader device or computer network, which would then compare collected data to threshold readings and generate notification messages to the individual, a caregiver, a work supervisor, or other device user. For example, an individual's sweat ion content could be indicated by directing a sweat sample flow across a plurality of electrodes that are configured to measure sweat conductivity; the individual's sweat onset and cessation can be indicated by measuring galvanic skin response (“GSR”); and the individual's sweat rate can be indicated by directing a sweat sample through a channel of defined volume containing a plurality of sweat-activated electrode switches. These three capabilities can be combined in a single device, which can use a volumetric sweat rate sensor to calibrate the individual's sweat conductivity and GSR measurements, and thereby provide useful information about the individual's physiological state, including sweat rate, sweat content, water loss, and dehydration state. The scope of the disclosed invention therefore comprises wearable devices configured to measure sweat conductivity, GSR, and/or volumetric sweat rate, devices that use volumetric sweat rate to calibrate, improve, and extend sweat conductivity and GSR measurements, and methods to accompany the use of such devices.